US researchers conducted telephone interviews with 787 women aged 60 to 80 years old in Cape Cod, Massachusetts, with breast cancer and 721 healthy women also in that age range.

The women were asked about their use of cleaning products and pesticides, and split into four groups ranging between high and low users. Cancer rates for the different groups were then compared.

Study leader Dr Julia Brody, from the Silent Spring Institute in Newton, Massachusetts, said: "Women who reported the highest combined cleaning product use had a doubled risk of breast cancer compared to those with the lowest reported use.

"Use of air fresheners and products for mould and mildew control were associated with increased risk. To our knowledge, this is the first published report on cleaning product use and risk of breast cancer."

Air fresheners were found to double breast cancer risk among women in the highest-use group, as did weekly use of mould and mildew-removing agents.

Many pesticides, household cleaners and air fresheners contain ingredients known to trigger breast cancer in animals, said the researchers.

Some were also made with endocrine (hormone) disrupting chemicals (EDCs) that could theoretically affect the growth of oestrogen-sensitive breast cancer cells.

Hormone-disruptors such as synthetic musks and phthalates were commonly used in air fresheners, said the scientists. Air fresheners may also contain chemicals called terpenes which can react with ozone in the air to form cancer triggers such as formaldehyde, benzene and styrene, they added.

"Although exposure levels may be low and EDCs are typically less potent than endogenous hormones, limited knowledge of product formulations, exposure levels and the biological activity and toxicity of chemical constituents alone and in combination make it difficult to assess risks associated with product use," the researchers wrote.

The scientists acknowledged that their results might be swayed by "recall bias" because they depended on answers to questions.

For instance, women who blamed chemical pollutants for their breast cancer might be more likely to report high usage of cleaning products.

However, Dr Brody said it was also true that women with cancer, who thought a lot about the likely cause of their disease, may be more likely to recall their use of cleaners accurately.

Such uncertainty could be avoided by a "prospective" study which followed the fate of a study group over a period of years.

"Because exposure to chemicals from household cleaning products is a biologically plausible cause of breast cancer and avoidable, associations reported here should be further examined prospectively," the researchers concluded.